Control apparatus



April 195.9 (2. J. BISHOFBERGER 2,882,371

CONTROL APPARATUS Filed Feb. 5, 1958 2 Sheets-Sheet 1 INVENTOR. CARL J.BISHOFBERGER A 7' TOR/VEY April 1959 c. J. BISHOFBERGER 2,882,371

CONTROL APPARATUS 7 Filed Feb. 5, 1958 2 Sheets-Sheet 2 F INVENTOR.

CARL J. BISHOFBERGER ATTORNEY United States Patent CONTROL APPARATUSCarl J. Bishofberger, Minneapolis, Minn., assignor toMinneapolis-Honeywell Regulator Company, Minneapolis, Minn, acorporation of Delaware Application February 5, 1958, Serial No. 713,476

7 Claims. (Cl. 200-138) The present invention is directed to a heatsensitive control device and specifically to the novel slip-friction andheat sink arrangement incorporated therein. Further, the invention isdirected to a heat sensitive control device incorporating a flat bimetalelement wherein means are provided to minimize wiping, between thecontact located on the bimetal element and a fixed contact, upon aflexing of the bimetal element.

In any device utilizing a bimetal for a heat sensitive device, one ofthe main problems encountered is in the provision of a sufl'icientlylarge bimetal element to provide the necessary output force but whichbimetal element is small enough so that its cost is minimized. It iswell recognized that in most heat sensitive devices the largest singlecost factor is the bimetal element. By providing proper design andminiaturization of parts of the heat sensitive device, the size of thebimetal element of the heat sensitive device can be maintained at aminimum.

Further, the miniaturization referred to above is important especiallywhen the heat sensitive device takes the form of a flame detector foruse with and when located within an oil burner blast tube, in that theair for the burner must pass through the blast tube and any impedimentsplaced in the air path interferes with the free flow of air, and henceinterferes with the flame pattern. Thus, the smaller the flame detector,the more eflicient the oil burner blast tube and the flame patternproduced thereby.

In the heat sensitive device disclosed herein, a novel slip frictionarrangement is shown, the elements of which are: easily formed, capableof being miniaturized, and devoid of close tolerances. Also, the uniquedesign of the slip friction arrangement allows for a reduced size of theentire heat sensitive device, and consequently, the allowability ofutilizing a relatively small piece of bimetal. The heat sensitive deviceis further characterized by the fact that while the bimetal is connecteddirectly to the slip friction arrangement and hence to the supporttherefor, these portions do not provide an effective heat sink inasmuchas a reduced connection between the bimetal and the slip frictionarrangement is utilized.

Further, since a flat bimetal element tends to bow or flex when exposedto a change in temperature, the provision of a contact on a flat,cantilever bimetal element, for cooperation with a fixed contact usuallyresults in the relative moving of the contacts and a Wiping there-'between. In certain applications, while a small amount of contactwiping is desirable to keep the contact surfaces clean, it is alsodesirable to keep the contact wiping to a minimum due to the arcingresulting between the contacts and the grinding of foreign matterbetween the contacts which results upon an excess of contact wiping. Asdisclosed herein, the bimetal element, and its associated contact, islocated with respect to the slip friction arrangement and the remainderof the construction so that with the contacts engaging each other andupon flexing of the bimetal element, the supported end of the bi-2,882,37l Patented Apr. 14, 1959 metal element moves toward the fixedcontact to compensate for a movement of the contact located on thebimetal element in the opposite direction caused by the flexing, therebyreducing contact wiping.

It is therefore an object of this invention to provide a heat sensitivedevice which permits the utilization of a relatively small piece ofbimetal.

Another object of this invention is to provide a slip frictionarrangement wherein the elements are small and easily formed and whichelements require no appreciable tolerances.

It is a further object of this invention to provide a heat sensitivedevice including a bimetal element and a support therefor wherein thesupport does not act effectively as a heat sink.

Still another object of this invention is to provide a heat sensitivedevice wherein the flat bimetal element thereof and the support thereforare so arranged with the contact on the bimetal element engaging a fixedcontact and upon a flexing of the bimetal that wiping of the contactlocated on the bimetal with the fixed contact is minimized due to acompensating movement introduced into the system.

These and other objects will become more apparent from a reading of thefollowing specification and appended claims in which:

Figure 1 is a perspective view of an oil burner blast tube assembly witha heat sensitive device in the form of a flame detector attached to anoil tube;

Figure 2 is a sectional view of the flame detector including a slipfriction arrangement and bimetal element associated therewith;

Figure 3 is a plan view of the arrangement of Figure 2 with the coverremoved;

Figure 4 is a view of a portion of the slip friction arrangement and thebimetal element;

Figure 5 is a plan view of the arrangement of Figure 4;

Figure 6 is a view of the arrangement of Figure 4 taken along the lines6-6 thereof; and

Figures 7-12 are views of the base of the flame detector showing theslip friction arrangement and the bimetal element during various stagesof the cycle of the flame detector.

In Figure 1 of the drawing a blast tube 10 of an oil burner is shown.Within the shell of the blast tube 10 are located an oil tube 12 havingan orifice 13, a pair of ignition electrodes 15 and 16, and a flamedetector 20. The flame detector 20 is mounted on the oil tube 12 bymeans of a bracket 19. The flame provided by the burning oil is locatedbeyond the opening 11 of the blast tube 10, and it is the radiation ofthis flame to which the flame detector 20 is responsive. The size of theflame detector 20 in relation to the inner cross sectional area of theshell of the blast tube 10 is such that it provides a minimumrestriction to the free flow of air which is desirable due to the effectsuch free flow has on the efliciency of the oil burner blast tube andthe flame pattern produced thereby.

It may be noted that the structure shown in the remainder of the figuresis approximately twice actual size and has been so shown for purposes ofclarity.

The flame detector 20 is more completely shown in Figures 2 and 3wherein a base 22 and a cover 29 are held together by fastening means25. A lime glass window 26, which is appropriately cemented in place,provides an opening through which radiation is allowed to pass to theinterior of the flame detector 20. The base 22 and the cover 29 areformed from ceramic materials and the mating edges thereof are groundflat. By administering a coat of heat resistance varnish to the jointbetween the base 22 and the cover 29, after assembly, a substantiallyair tight container is provided.

r 2,882,371 I s r K A contact support member 30 is aflixed to the baseby a first terminal member 31. To the contact support member 30, acontact 32 is aflixed and directly above the contact 32, an insulatingmember 34 is located. The contact 32 and insulating member 34 serve asstops for a flat bimetal member 35 and specifically a contact member 36located .at its free end. The bimetal 35 is affixed at its opposite endto ,a portion 39 of a force input member in the form of a channel shapedyoke member 4t).

The yoke member -40 includes a pair of arms 41 and 4-2 extending in thesame general direction and connected by a portion 43. The arms 41 and 42are disposed between the arms 45 and 46 of the support member in theform of a bifurcated frame 47 which is affixed to the base 22 by meansof a second terminal member 49. A bar or shaft 50 is disposed throughoblong openings 44 of arms 41 and 42 :of yoke :member 40, theextremities of which bar are supported between the bendable ears of thearms 45 and 46 of the frame 47. It should be noted that the shaft 50 iscylindrical in shape throughout almost all its length to allow the yokemember 40 to rotate thereabout, but is oblong in shape where disposed inthe arms 45 and 46 of the frame 47, as more clearly shown in Figure 9,so as to make it non-rotatable.

A resilient member in the form of a substantially V- shaped spring 53includes a first arm 54 which is operatively fastened to the connectingportion 43 of the yoke member 40 and a second arm 55 which is bent overthe top of connecting portion 43 and biased against the shaft 50.

Lead 58 is fastened to the lower surface of the bimetal 35 and to theuppermost portion of the second terminal member 49, thereby allowing forthe establishment of a circuit across the first terminal member 31 andthe second terminal member 4-9 upon the contact 36 of the bimetal 35engaging the fixed contact 32.

In Figures 4-6 the bimetal 35 and yoke member 41 subassembly isseparately shown. The shape and location of the oblong openings 44 ofarms 41 and 42 is clearly shown in Figures 4 and 6. As is indicated inFigure '5, an extension 59 joining the portion 39 and the connectingportion 43 is necked down, so as to limit the transfer of heat betweenthe bimetal 35 and yoke member 40, spring 53, shaft 50, and frame 47.This construction therefore acts to reduce the heat sink poten tialtiesof the aforementioned members which of course is desirable in a devicesuch as described herein due to the lag introduced into the device byuninhibited heat transfer. In Figure 6, the relation of the necked downportion 59 to the remainder of the yoke member 40 is brought forth ina'clearer manner.

An examination of Figures 2-6 will indicate that the flame detectordescribed is comprised of relatively easily formed elements, whichelements require no close tolerances and which elements can beminiaturized. Further, the assembly of the elements is simple andstraightforward. Thus, the shaft '50 need but be passed through theoblong openings 44 of the arms 41 and 42 of yoke member 40 and thesubassembly dropped in place between the bendableears of the arms 45 and46 of the frame 47 whereupon a consequent bending of the bendable earsof the arms 45 and 46 to the position shown in Figure 2 and the affixingof the complete assembly to the base 22 in cooperative relation with thecontact support member 30 completes the device, except for fastening ofthe cover 29 thereto.

The slip friction arrangement of the flame detector is comprised of: theframe 47, the nonrotatable shaft '50, the yoke member 40, and the spring53, interrelated as indicated above. An initial predetermined amount offorce applied to the yoke member 43 by some means such as the bimetal 35does not result in a rotational movement of the yoke member 40 about theshaft 50. This is becauseof the bias set up between the yoke member 40and the shaft 50 by the spring 53. Upon a predetermined input forcebeing :applied to the yoke member 40, rotation of the yoke member 40about the shaft 50 occurs with the consequent slip friction between theyoke member 40 and the shaft 50 arising. Should the input force beremoved from the yoke member 40 no movement of the yoke member 40 takesplace due to the bias set up between the yoke member 40 and the shaft 50by the spring 53. Further, a counter action will not cause rotation ofthe yoke member in the appropriate direction until a predetermined inputforce is obtained to overcome the aforementioned bias.

The operation of the flame detector will now be under taken andreference should be made to Figures 7-12.

In Figure 7, the arrangement is shown when cool and with the contact 36of the bimetal 35 engaging the insulating member 34 with little or noloading of the slip friction arrangement. The bimetal 35 is so arrangedthat upon an increase in radiation being directed toward the flamedetector, and hence an increase in temperature being sensed by thebimetal, the bimetal begins to flex and move downwardly toward the fixedcontact 32 without a consequent movement of the slip frictionarrangement, as shown in Figure 8. Upon a further increase in radiation,contact 36 of the bimetal 35 engages the contact 32 to close a circuit,as shown in Figure 9 thereby resulting in a control function takingplace. Again, no movement of the slip friction arrangement takes place.Should the radiation continue to increase, increased flexure of thebimetal 35 occurs. This increased flexure results in a loading betweencontacts 32 and 36 and of the slip friction arrangement until apredetermined level is attained. Upon a further increase in radiation,the slip friction arrangement comes into play in that the bias providedby spring 53 is overcome and the yoke member 40 rotates clock-wise aboutthe shaft 50, as is shown in Figure 10, thereby limiting the loading towhich the contacts 32 and 36 are subjected.

Now, it will be noted that upon engagement between contacts 32 and 36,increased flexure of the bimetal 35 tends to cause relative movementbetween contacts 32 and 36 and movement of contact 36 toward shaft 50.However, due to the relation of the portion 39 of yoke member 40 withrespect to shaft 50, rotation of the yoke member 40, and hence of thesupported end of the bimetal 35 is in a direction so as to result inmovement of the supported end of the bimetal toward the contact 32.'These opposing, compensating movements result in a minimization ofcontact Wiping.

With a flame detector for use with an oil burner, it is of coursenecessary to almost instantly sense any reduction in radiation directedtoward the flame detector. With the present device, a reduction inradiation results initially in a removal of the loading between thecontacts 32 and 36 and of the slip friction arrangement and subsequentlyin a movement of the bimetal 35 and associated contact 36 away from thecontact 32 toward the insulating member 34, as shown in Figure 11, toopen the circuit, thereby resulting in a control function. It will benoted that the yoke member 40 does not rotate in the opposite directionunder this set of circumstances due to the bias set up between the yokemember 40 and shaft 50 by the spring 53. The bimetal 35 is still flexedinasmuch as the radiation has been merely reduced and the temperature ofthe bimetal is still higher than that experienced by the device underthe conditions of Figure 7. In Figure 12, the bimetal 35 is returned tothe initial position so that contact 36 engages insulating member 34.However, the bimetal 35 is still flexed, again due to the fact that theradiation received by it is higher than when under the conditions ofFigure 7. Should a continuing decreasein radiation be received by thedevice, the bimetal 35 would .approach the position shown in Figure 7,with a tendency to flex in the opposite direction to cause acounterclockwise rotation of the yoke member 40 about shaft 50 and toeventually cause a similar loading only in the opposite direction of theslip friction arrangement,

for the bimetal support structure to be effectively by-,

passed as a heat sink. While only one modification has been shown of thestructure, other modifications are of course possible, and therefore,the scope of the invention is to be determined from the following claimsin which I claim:

1. A flame detector of the radiation sensitive bimetal type for use witha flame producing unit, the combination comprising: a cover including aglass window for the passage of radiation; a base member affixed to saidcover; a bifurcated support member located within the enclosure formedby said cover and said base and affixed to said base; a channel shapedyoke member including a pair of arms extending in the same generaldirection each having an oblong opening and a portion connecting saidarms, said yoke member including an extension integral and connected bya necked down portion with the portion of said yoke member connectingthe arms thereof; a shaft nonrotatably held by the arms of said supportmember, said yoke member being rotatably supported on said shaft by saidoblong openings; a flat bimetal element having a first end portionoperatively connected to the extension of said yoke member and locatedwith respect to the window of said casing so as to be exposed toradiation passed therethrough, a second end portion of said bimetalelement including a contact being associated with stop means including acontact supported by said base; and a substantially V-shaped springmember having a first portion operatively connected to the portion ofsaid yoke member connecting the arms thereof and a second portion biasedtowards and engaging said shaft; initial flexure of said bimetal elementresulting in the second end thereof being moved toward and engaging saidstop means without consequent rotation of said yoke member due to theaction of said spring member against said shaft and further flexure ofsaid bimetal element after the contact of said stop means is encountered by the contact thereof resulting in rotation of said yoke memberabout said shaft; the extension of said yoke member and said stop meansbeing located with respect to each other and said shaft so that uponflexure of said bimetal element and rotation of said yoke member thefirst end portion of said bimetal element moves toward said stop meansthereby compensating for movement of the second end portion of saidbimetal element toward said shaft caused by flexure of said bimetalelement to reduce contact wiping.

2. A flame detector of the radiation sensitive bimetal type for use witha flame producing unit, the combination comprising: a cover including aglass window for the passage of radiation; a base member afiixed to saidcover; a bifurcated support member located within the enclosure formedby said cover and said base and aflixed to said base; a channel shapedyoke member including a pair of arms extending in the same generaldirection and a portion connecting said arms, said yoke member includingan extension integral with the portion of said yoke member connectingthe arms thereof; a shaft nonrotatably held by the arms of said supportmember, said yoke member being rotatably supported on said shaft byopenings located in said arms, a flat bimetal element having a first endportion operatively connected to the extension of said yoke member andlocated with respect to the window of said casing so as to be exposed toradiation passed therethrough, a second end portion of said bimetalelement being associated with stop means supported by said base; and aspring member having a first portion operatively associated with theportion of said yoke member connecting the arms thereof and a secondportion biased toward and engaging said shaft; initial flexure of saidbimetal element resulting in the second end thereof being moved towardand engaging said stop means without consequent rotation of said yokemember due to the action of said spring member against said shaft andfurther flexure of said bimetal element after said stop means areencountered thereby resulting in rotation of said yoke member about saidshaft.

3. A heat sensitive device comprising: a base; a bifurcated supportmember aflixed to said base; a channel shaped yoke member including apair of arms extending in the same general direction and a portionconnecting said arms; a shaft nonrotatably held by the arms of saidsupport member, said yoke member being rotatably supported on said shaftby openings located in said arms; said yoke member including anextension integral with the portion of said yoke member connecting thearms thereof and displaced from the axis of rotation thereof; and a fiatbimetal element having a first end portion operatively connected to theextension of said yoke member and having a second end portion includinga contact associated with stop means including a contact located on saidbase; the extension of said yoke member and said stop means beinglocated with respect to each other and said shaft so that flexure ofsaid bimetal element after the contact of said stop means is encounteredby the contact thereof results in rotation of said yoke member aboutsaid shaft and movement of said extension and the first end portion ofsaid bimetal element toward said stop means thereby compensating formovement of the second end portion of said bimetal element toward saidshaft caused by flexure of said bimetal element to reduce contactwiping.

4. A heat sensitive device comprising: a base; a support member affixedto said base; a bar nonrotatably held by said support member; a forceinput member supported and rotatable about said bar; and a flat bimetalelement having a first end portion operatively connected to said forceinput member displaced from the axis of rotation thereof and having asecond end portion including a contact associated with stop meansincluding a contact located on said base; said force input member andsaid stop means being located with respect to each other and said bar sothat flexure of said bimetal element after the contact of said stopmeans is encountered by the contact of said bimetal element results inrotation of said force input member about said bar and movement of saidforce input member and the first end portion of said bimetal elementtoward said stop means thereby compensating for movement of the secondend portion of said bimetal element toward said bar caused by flexure ofsaid bimetal element to reduce contact wiping.

5. A slip friction arrangement comprising: a bifurcated support member;a channel shaped yoke member including a pair of arms extending in thesame general direction each having an oblong opening and a portionconnecting said arms, a shaft nonrotatably held by the arms of saidsupport member, said yoke member being rotatably supported on said shaftby said oblong openings; and a substantially V-shaped spring memberhaving a first arm operatively connected to the portion of said yokemember connecting the arms thereof and a second arm disposed betweensaid yoke member and said shaft, said second arm being biased againstsaid shaft thereby tending to force the yoke member to a positionwhereby said shaft engages one extremity of the oblong openings of thearms of said yoke member and further tending to retard rotation of saidyoke member about said shaft.

6. A slip friction arrangement comprising: a bifurcated support member;a channel shaped yoke member including a pair of arms extending in thesame general direction and a portion connecting said arms, a shaftnonrotatably held by the arms of said support member, said yoke memberbeing rotatably supported on said shaft by openings located in saidarms; and a spring member having a first 'portion operatively connectedto the portion of said yoke member connecting the arms thereof and asecond portion disposed between said yoke member and said shaft, saidsecond portion being biased against said shaft thereby tending to retardrotation of said yoke member about said shaft.

7. A heat sensitive device comprising: a base, slip friction'meanshaving a stationary mernber aflixed to said 10 base and rotatable meansmounted on said stationary member having an axis of rotation, asubstantially fiat bimetal element having a first portion mounted onsaid rotatable means and displaced a given distance from said axis ofrotation, said bimetal element having a second portion including acontact assembly cooperating with stop 8 means including a stationarycontact mounted on said b e, e leng h f id m l l m n e said firs andsecond portions being related to said given distance vof displacement sothat continued flexure of said bimetal References Cited in the file ofthis patent UNITED STATES PATENTS 2,660,645 Deubel Nov. 24, 1953

